This application claims the priority of Korean Patent Application No. 2003-45407, filed on Jul. 4, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a switching mode power supply (SMPS) powering electronic devices, and more particularly, to a power circuit protection apparatus halting an operation of a pulse width modulation (PWM) controller in a case where an abnormal state is generated due to an open or short in a secondary side winding of a transformer.
2. Description of the Related Art
In general, an SMPS using a pulse width modulation (PWM) method has controlled a power source of an electronic device by realizing line regulation in a primary side winding of the power source and load regulation in a secondary side winding of the power source using a PWM controller.
In general, an SMPS obtains direct current (DC) power by directly rectifying and filtering a common use alternating current (AC) power and converting the DC voltage into a high frequency square wave.
Also, after the SMPS conducts the voltage having a square waveform to an insulating transformer having a certain winding ratio, the SMPS converts the voltage into a DC voltage by rectifying and filtering the voltage waveform of a secondary side winding of the insulating transformer. Here, the SMPS is made so as to control an on/off time of a semiconductor device for switching in order to supply a constant DC voltage to a load.
The SMPS performs line regulation by sensing a current from an output signal of a switching unit controlled by a PWM controller and load regulation by detecting a voltage variation induced by coils of loads on a secondary side of the power supply and compensates a voltage of the secondary side of the power supply by feeding back the result of the line regulation and the load regulation to the PWM controller.
FIG. 1 is a block diagram of a conventional switching mode power supply (SMPS).
With reference to FIG. 1, the SMPS includes an AC input unit 100, a rectifier 101, a transformer 102, a switching unit 103, a PWM controller 104, a current sensing unit 105, an output unit 106, and an initial driving unit 107.
The AC input unit 100 inputs an AC voltage from the outside and conducts the AC voltage to the rectifier 101.
The rectifier 101 rectifies the AC voltage conducted from the AC input unit 100 into a DC voltage and outputs the DC voltage to a primary side coil of the transformer 102.
The transformer 102 inputs the DC voltage from the rectifier 101, is controlled by a switching control signal conducted from the switching unit 103, and induces a predetermined voltage in a secondary side coil of the transformer 102.
The output unit 106 rectifies and smoothes the voltage induced in the secondary side coil of the transformer 102 and outputs a predetermined voltage Vout. The output unit 106 includes a rectifying diode D1 and a smoothing condenser C2 for rectifying and smoothing the voltage induced in the secondary side coil of the transformer 102.
The switching unit 103 includes a switching component such as a field effect transistor (FET), and the on/off time of the switching unit 103 is controlled by a PWM signal output from the PWM controller 104. Therefore, the switching unit 103 controls outputs of the transformer 102 by the PWM signal output from the PWM controller 104.
The current sensing unit 105 senses an output current of the switching unit 103 and conducts the sensed current to the PWM controller 104.
The PWM controller 104 receives the generated voltage error by sensing the voltage Vout output from the output unit 106, receives the output current of the switching unit 103 sensed through the current sensing unit 105, and outputs a PWM signal with adjusted duty rate to the switching unit 103.
The initial driving unit 107 supplies a driving voltage for initial driving of the PWM controller 104 by rectifying an initial AC input voltage.
The description of an SMPS is disclosed in U.S. Pat. No. 6,510,066.
In general, in a power supply of a plasma display panel (PDP), due to a high voltage supplied as a sustain power and a high load current, a power source is supplied using two transformers, not one transformer as shown in FIG. 1. However, in a case where a voltage of one of the two transformers falls below a predetermined voltage, or a case where balance of the two transformers is not matched, the other one transformer must cover the capacity of the two transformers.